1. Field of the Invention
The present invention relates to a system and method for providing route information to a driver of a vehicle.
2. Background Art
With the ever increasing need to produce vehicles that are more fuel efficient, hybrid electric vehicles (HEV's) have provided an improvement in fuel economy over many conventional vehicles that utilize only an internal combustion engine to drive the vehicle. One of the primary advantages of an HEV is that it allows the vehicle to be powered by one or more electric motors under certain operating conditions. For example, if the speed of the vehicle is relatively moderate, and the battery or other electrical power sources sufficiently charged, the engine may be shut off, and the vehicle powered exclusively by the electric motors. As operating conditions change, the engine may be started to provide additional power, and if needed, operate a generator to charge the battery.
In order to ensure that the battery has enough power to perform desired functions—e.g., operate a generator to start the engine, or provide power to a motor to provide torque to the vehicle wheels—a state of charge of the battery is maintained within a predetermined range. For example, if the state of charge drops below a certain value, the engine may be started to drive a generator to charge the battery. Operation of the engine consumes fossil fuel, and produces undesirable emissions.
Conversely, if the state of charge rises above a certain level, additional charging may be undesirable. In such a case, additional charging of the battery is rejected. Therefore, if the vehicle is slowed or stopped—a situation that may typically call for the capture of regenerative braking energy—the vehicle's friction brakes may be used so that the battery is not overcharged. This is inefficient, as the energy available from the braking operation is lost.
The temperature of a battery can also affect its ability to accept charge and deliver power. For example, if a battery is relatively cold, it may be able to accept charge and deliver power, but it may do so very slowly—this can be inefficient. In the case of a battery being too warm, charging or discharging may damage the battery, and so various control mechanisms may be in place to ensure that the battery does not receive charge or deliver power when it is above a certain temperature. This too is inefficient, particularly in the case of HEV's, where the engine may need to be run merely because the battery is too warm.
The temperature and SOC of a battery can be affected by many factors, including driving habits and external conditions. For example, weather conditions—e.g., ambient temperature—can affect the state of the HEV's powertrain, and specifically the battery, throughout a drive. Another factor influencing driving efficiency is traffic conditions. Such conditions can include, for example, the speed of traffic flow, traffic control factors such as stop signs and street lights, and the presence of obstacles such as construction zones. Moreover, the position of a vehicle vis-à-vis other vehicles—i.e., is the vehicle following other vehicles or driving freely—can influence the control strategy used to optimize performance and fuel economy.
Often there are multiple routes from a traveling vehicle's current location to its destination, and the choice of route affects the conditions that are encountered, and the order in which they are encountered. The conditions influence the driver's behavior, and consequently, vehicle operating efficiency and travel time. Moreover, each driver may have different preferences between reducing travel time and increasing operating efficiency. Indeed, the same driver may have one set of preferences for one trip, and another set of preferences for another trip.
Therefore, a need exists for a system and method for providing route information to a driver of a vehicle that is at least partly based on various external conditions, and also takes into account the driver's preferences for such things as time to reach destination and fuel efficiency.